The present disclosure generally relates to corrosion and, more specifically, to methods for suppressing corrosion of steel surfaces during subterranean treatment operations.
Treatment fluids can be used in a variety of subterranean treatment operations. Such treatment operations can include, without limitation, drilling operations, stimulation operations, production operations, remediation operations, sand control treatments, and the like. As used herein, the terms “treat,” “treatment,” “treating,” and grammatical equivalents thereof refer to any subterranean operation that uses a fluid in conjunction with achieving a desired function and/or for a desired purpose. Use of these terms does not imply any particular action by the treatment fluid or a component thereof, unless otherwise specified herein. More specific examples of illustrative treatment operations can include, for example, drilling operations, fracturing operations, gravel packing operations, acidizing operations, scale dissolution and removal operations, sand control operations, consolidation operations, and the like.
Corrosive environments comprising an acid can cause severe corrosion damage to many types of metal surfaces. As used herein, the term “corrosion” and grammatical variants thereof will refer to any reaction between a metal surface and its surrounding environment that causes a deterioration or change in the metal surface's properties or morphology. Examples of corrosion damage to a metal surface can include, but are not limited to, rusting, metal dissolution or erosion, pitting, peeling, blistering, patina formation, cracking, embrittlement, and any combination thereof.
Acidic treatment fluids are frequently utilized in the course of conducting various subterranean treatment operations. Illustrative uses of acidic treatment fluids during subterranean treatment operations include, for example, matrix acidizing of siliceous and/or non-siliceous formations, scale dissolution and removal operations, gel breaking, acid fracturing, and the like. When acidizing a non-siliceous material such as a carbonate material, mineral acids such as hydrochloric acid may often be sufficient to affect dissolution. Organic acids may be used in a similar manner to hydrochloric acid when dissolving a non-siliceous material. Siliceous materials, in contrast, are only readily dissolvable using hydrofluoric acid, optionally in combination with other acids. Illustrative siliceous materials can include, for example, silica, silicates, aluminosilicates, and any combination thereof, optionally in further combination with a non-siliceous material, such as a carbonate material.
Corrosion of metal surfaces within a wellbore penetrating a subterranean formation, such as tubulars and tools, for example, can be highly undesirable due to the difficulty, cost and production downtime associated with replacing or repairing such components. In many instances, elevated temperatures within subterranean formations can dramatically accelerate downhole corrosion rates. Localized temperature variations can also dramatically alter the rate at which corrosion takes place in a particular position within the wellbore.
Metal surfaces in fluid communication with a wellbore can similarly be susceptible to corrosion and its undesirable effects. In subsea wellbores, for example, a subsea riser structure extending from the wellbore to a platform or vessel on the ocean's surface or just below the ocean's surface can be susceptible to corrosion, in spite of the low temperatures of deepwater environments. Outside the wellbore, corrosion can occur during introduction of a treatment fluid to the wellbore, during production, or any combination thereof. Regardless of its location, corrosion-induced damage of a metal surface can represent a significant safety and/or environmental concern due to potential well failure issues.
Although acids may represent a potential corrosion threat to assorted metal surfaces, hydrofluoric acid can be especially problematic and damaging toward many metals due to its high reactivity. Various types or grades of steel represent illustrative metal surfaces that are particularly sensitive toward hydrofluoric acid. Most steel types are prone to corrosion in the presence of even modest quantities of hydrofluoric acid at pH values of about 7 or less, although the corrosion rates may vary significantly from type to type. The sensitivity of steel toward hydrofluoric acid can preclude use of this metal in situations where acidizing of a siliceous material is anticipated to take place. For example, the presence of steel within at least a portion of a subsea riser structure can preclude transport of hydrofluoric acid to or from a deepwater wellbore. Due to the propensity of steel surfaces toward corrosion by hydrofluoric acid, it can be especially difficult to conduct stimulation operations in deepwater wellbores containing a siliceous material.
In some instances, corrosion inhibitors can be used to reduce the propensity of a metal surface to undergo corrosion-induced damage by acids. As used herein, the terms “inhibit,” “inhibitor,” “inhibition” and other grammatical forms thereof will generally refer to the lessening of the tendency of a phenomenon to occur and/or the degree to which that phenomenon occurs. The terms “suppress,” “suppression” and other grammatical forms thereof may be used equivalently herein. The term “inhibit” and equivalents thereof do not imply any particular extent or amount of inhibition or suppression unless otherwise specified herein. Although the corrosiveness of hydrochloric acid toward steel can usually be effectively suppressed using a variety of common corrosion inhibitors, such corrosion inhibitors are often much less effective for inhibiting the corrosiveness of hydrofluoric acid. Moreover, due to the variance of corrosion rates for different types of steel and also factoring in the local conditions where the steel is present, it can be difficult to suppress corrosion using a single corrosion inhibitor that is effective over a range of conditions and metallurgies.